MRI is an imaging method which magnetically excites nuclear spin of an object placed in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation. The above-described MRI means magnetic resonance imaging, the RF pulse means a radio frequency pulse, and the MR signal means a nuclear magnetic resonance signal.
Here, an RF (Radio Frequency) coil is a coil device which applies an RF pulse to nuclear spin inside an object by, for example, supplying a coil with an RF pulse electric current and receives generated echo signals as MR signals.
RF coils are classified into the following three types in terms of transmission and reception: a transmit-only RF coil, a receive-only RF coil, and a dual-purpose RF coil used for application of RF pulses and reception of MR signals. In addition, RF coils are also classified into a whole body type and a local type.
Since MR signals emitted from an object are weak, it is preferable to receive MR signals at a position as close to the object as possible. Thus, various types of the local RF coils, each of which is shaped so as to fit each part of a human body, are used depending on an imaging part.
In MRI, multi-channel structure has been developed in an acquisition system of MR signals. The above-described channel means each of pathways of MR signals outputted from each of coil elements and inputted to an RF receiver of an MRI apparatus. The number of channels is set to equal to or smaller than the input reception number of the RF receiver.
If the number of cables between an RF coil and a control side of an MRI apparatus such as an RF receiver side increases due to development of the above-described multichannel structure, it is inconvenient because hard-wiring becomes complicated. Thus, wireless RF coils which unwire transmission and reception of data between an RF coil and a control side of an MRI apparatus are developed.
A significant number of coil elements are included in a wireless RF coil attached to an object. In addition, when plural wireless RF coils are attached to an object, the number of coil elements further increases.